1. Field of the Invention
The present invention relates to a plasma processing method.
2. Description of the Related Art
During the process of manufacturing a semiconductor device, a technology whereby an opening pattern is formed, for instance, at a layer insulating film of a workpiece by implementing a plasma etching process on the workpiece is adopted in the prior art. In this process, a photoresist film formed on the layer insulating film is used as a mask. Under normal circumstances, the photoresist film must be removed after the etching process. Accordingly, the processed workpiece is delivered into the processing chamber of an ashing apparatus from the etching apparatus. After the workpiece is brought in, the pressure of the atmosphere inside the processing chamber is sustained at a level equal to or higher than 300 mTorr (40.0 Pa) through induction of a processing gas and vacuum drawing. In addition, the workpiece is heated to a temperature equal to or higher than 150xc2x0 C. When the various conditions have been established, the processing gas inside the processing chamber is raised to plasma to ash the photoresist film.
A technology for achieving faster semiconductor device operation by utilizing a film constituted of a material achieving a low dielectric constant (hereafter referred to as a xe2x80x9cLow-Kxe2x80x9d) instead of the SiO2 film used in the prior art as the layer insulating film has been proposed in recent years. However, a process performed under high-pressure conditions such as the ashing process in the prior art described above causes a change in the properties of the Low-K film, and its dielectric constant becomes higher. This poses a problem in that a faster semiconductor device operation cannot be achieved even when a Low-K film is used to constitute the layer insulating film.
In addition, a Low-K film normally absorbs moisture readily. When the Low-K film is patterned through an etching process, a portion of the Low-K film becomes exposed. This results in a problem that when the workpiece is exposed to the atmosphere while it is delivered from the etching apparatus to the ashing apparatus as described above, the Low-K film absorbs the moisture in the atmosphere and the dielectric constant of the Low-K film rises.
An object of the present invention, which has been completed by addressing the problems of the prior art discussed above, is to provide a new and improved plasma processing method that eliminates the problems above and other problems as well.
In order to achieve the object described above, the present invention provides a plasma processing method comprising a step in which a plasma etching process is implemented on a workpiece placed inside a processing chamber by using a photoresist film on an organic polysiloxane film formed at the workpiece to form a pattern in which a portion of the organic polysiloxane film is exposed and then the photoresist film is removed, a step in which a processing gas is induced into the processing chamber and the pressure inside the processing chamber is set within a range of 30 mTorr (4.00 Pa)xcx9c150 mTorr (20.0 Pa) and a step in which the processing gas is raised to plasma at the pressure thus set to remove the photoresist film from the workpiece on which the pattern has been formed, as disclosed in claim 1.
The workpiece to undergo the process according to the present invention has already undergone an etching process with at least the opening portion of the pattern formed at the organic polysiloxane film exposed. Organic polysiloxane constituting the film achieves the structure expressed in the following chemical formula, having an organic functional group containing a C atom and an H atom and O atoms bonded with an Si atom. (Chemical formula 1) 
It is to be noted that the organic functional group represented as R in the chemical formula above may be any of alkyl groups such as a methyl group, an ethyl group and a propyl group and their derivatives or any of the alkyl groups such as phenyl radicals and derivatives. The C atom constituting the organic functional group is separated from the Si atom when the photoresist film on the organic polysiloxane film is removed at high pressure as in the method in the prior art. This results in a change in the molecular structure of the organic polysiloxane and the low dielectric constant characteristics unique to the organic polysiloxane film are lost. For this reason, according to the present invention, an ashing process is implemented under a pressure level set within the range of 30 mTorr (4.00 Pa)xcx9c150 mTorr (20.0 Pa) in which the C atom is not separated from the Si atom. Thus, the molecular structure of the organic polysiloxane is maintained even after the ashing process, thereby assuring the low dielectric constant characteristics of the organic polysiloxane film. As a result, by using the organic polysiloxane film to constitute a layer insulating film, for instance, a fast semiconductor device operation is achieved.
In addition, it is desirable to set the pressure inside the processing chamber within the range of 50 mTorr (6.66 Pa)xcx9c100 mTorr (13.3 Pa) as disclosed in claim 2, for instance. By implementing the ashing process at such a pressure, changes in the film properties of the organic polysiloxane film can be inhibited even more effectively.
It is also desirable to perform the step for removing the photoresist film in the same processing chamber where the plasma etching process has been performed, as disclosed in claims 3 and 4, for instance. Since this eliminates the need for the workpiece to be carried out of the processing chamber during the period of time elapsing between the end of the etching process and the start of the ashing process, the workpiece is never exposed to the atmosphere. As a result, the exposed organic polysiloxane film does not absorb any moisture from the atmosphere, thereby preventing the dielectric constant of the organic polysiloxane film from the increasing.